Some red winemakers deliberately delay fermentation for several days after crushing, holding the must cold. The purpose is to extract in a different solvent than the one fermentation provides.
Water and alcohol dissolve different things
Before fermentation begins, the liquid surrounding the skins is essentially grape juice, which is water-based. Alcohol only appears once yeast starts working, and until then the solvent is unchanged.
Water-soluble compounds include many colour pigments and a set of fresh, primary aromatic compounds. These dissolve readily during a cold soak and accumulate in the juice over several days.
Tannin, by contrast, is far more soluble in alcohol. Delaying fermentation therefore extracts colour and aroma while leaving much of the tannin behind for now.
Cold is what keeps the yeast waiting
Yeast activity slows dramatically at low temperatures, so chilling the must to near refrigeration levels holds fermentation off for days.
Cellars achieve this with jacketed tanks, with dry ice added directly to the must, or simply by harvesting at night and processing cold fruit.
The wine is exposed to spoilage risk during this window, since no alcohol is present to protect it. Sulphur dioxide and strict temperature control are the usual safeguards.
What it does to the finished wine
The typical result is deeper colour and a more pronounced fresh fruit character. Tannin arrives later in the process and tends to feel more supple in the finished wine.
Because pigments extracted early have longer to bind with tannin during fermentation, colour stability over time often improves as well. The wine holds its hue further into bottle age.
The effect is more obvious in lightly pigmented varieties, where every additional degree of colour extraction is visible in the glass.
Why it is not universal
Cold soaking occupies tank space during the busiest weeks of the year, and tank space during harvest is the scarcest resource a winery has.
It also requires cooling capacity, which is a significant capital cost for a small producer working with ambient cellar temperatures.
Some winemakers argue the technique produces a flattering early impression that fades with bottle age. The disagreement is genuine rather than settled.
The mirror image at the other end
A related decision happens after fermentation, when the wine can be left in contact with the skins for additional weeks.
That extended maceration extracts in alcohol rather than water, and it works on tannin, polymerising it into longer, softer chains.
Producers therefore have two levers on either side of fermentation, one shaping colour and aroma and the other shaping structure. Most use one, some use both.